SUMMARY: Acute lung injury (ALI) is a devastating complication of sepsis,viral and bacterial pneumonias, severe trauma with or without major blood loss, acid aspiration and other conditions that affect the lung either primarily or secondarily.This relatively common syndrome (~200,000 cases per yr in the US) currently has an overall mortality rate of ~40%. Lung inflammation associated with the production of reactive oxygen species (ROS) is an important contributor to the ALI syndrome. We have shown that activation of NADPH oxidase, type 2 (NOX2), the major source of ROS in lungs, requires the PLA2 activity of peroxiredoxin 6 (Prdx6) and have recently identified a 9 amino acid peptide that binds to Prdx6 and inhibits its PLA2 activity; we have named this Prdx6 inhibitory peptide (PIP-2). PIP-2 encapsulated in liposomes and administered intratracheally (IT) to mice inhibited the lung generation of ROS by >80% for 24 h. PIP-2 administered 12-16 h after low dose LPS (given IT) markedly decreased lung inflammation and tissue oxidative injury when examined at 24 h and greatly decreased mortality (from 100% to 28%) after high dose LPS. PIP-2 also markedly decreased mouse mortality after intraperitoneal LPS as a model of sepsis. We now propose to evaluate the effect of PIP-2 on lung injury in 2 mouse models of ALI associated with infection. The first will be the Klebsiella pneumoniae infection model (Sp.Aim 1); the 2nd model will be the cecal ligation and puncture (Sp. Aim 2). PIP-2 will be administered at either 12 or 24 hrs after the bacterial insult. We will evauate the effect of PIP on lung inflammation, disruption of the blood-gas barrier,and oxidative injury. We also will determine the effect of PIP on lung bacterial load as the NOX2 inhibitor may interfere with PMN bactericidal mechanisms. We propose that PIP-2 will have clinical application for the prevention of lung inflammation and tissue oxidative injury that are major contributors to the pathogenesis of ALI. We plan a phase 2 STTR application to evaluate the effect of PIP treatment on more complex models of acute lung injury in large animal models and to determine possible toxicological effects of peptide administration.